- An abscess is collection of pus within soft tissues
- Occurs when hosts response to infection is inadequate
- Predisposing factors include foreign bodies, haematoma formation and
poor blood supply
Pathology
- An abscess contains bacteria, acute inflammatory cells, protein
exudate and necrotic tissue
- It is surrounded by granulation tissue (the 'pyogenic membrane')
- The organisms usually involved are:
- In superficial abscesses - Staph. aureus, Strep. pyogenes
- In deep abscesses - Gram negative species (e.g. E. coli)
and anaerobes (e.g. Bacteroides)
Clinical features
- Superficial abscesses include infected sebaceous cysts, breast and
pilonidal abscesses
- Show cardinal features of inflammation - calor, rubor, dolor, tumor
- Heat
- Redness
- Pain
- Swelling
- After a few days superficial abscess usually 'point' and are
fluctuant
- Deep abscesses include diverticular, subphrenic and anastomotic
leaks
- Patients shows signs of inflammation - swinging pyrexia,
tachycardia, tachypnoea
- Physical signs are otherwise difficult to demonstrate
- Site of abscess may not be clinically apparent
- Radiological imaging often required to make the diagnosis
Treatment
- All abscesses require adequate drainage
- Should be performed under general anaesthesia
- Antibiotics have little to offer as tissue penetration is usually
poor
- Prolonged antibiotic treatment can result in a chronic inflammatory
mass (an 'antibioma')
- Superficial abscesses are usually suitable for open drainage
- For deep abscesses closed drainage may be attempted
Open technique
- Superficial abscesses can usually be drained through a cruciate
incision
- Position of incision may allow depended drainage
- Pus should be sent for microbiology
- Loculi should be broken down and necrotic tissue excised
- A dressing should be inserted into the wound
- Packing is not required - it is painful
Closed techniques
- Deep abscess can be treated by ultrasound or CT guided aspiration
- Success can not always be guaranteed
- Multiloculated abscesses may not drain adequately
- Percutaneous access my be difficult because of the position of
adjacent organs
Psoas abcess
- The iliopsoas compartment is extraperitoneal space
- Contains the psoas and iliacus muscles
- Psoas lies close to abdominal structures and organs (e.g. sigmoid
colon, ureter, appendix)
- Infection in these structures can spread to the muscles
- Muscles have good blood supply predisposing to haematogenous spread
of infection
Aetiology
- Psoas abscess can be classified as primary or secondary
- Primary abscess occur as a result of haematogenous spread of
infection
- Seen in conditions in which patients are immunocompromised such as:
- Diabetes mellitus
- Intravenous drug abuse
- AIDS
- Renal failure
- Secondary abscess are associated with local pathology
- Common causes include
- Crohn's disease
- Diverticulitis
- Appendicitis
- Urinary tract infection
- Septic arthritis
- Femoral vessel cannulation
- In developing countries most abscesses are primary
- In western countries about 60% of abscess are secondary
- Staph aureus is the commonest causative organism in primary
abscess
- Gut-related organisms are the commonest cause of secondary abscess
- Tuberculosis is a rare cause of psoas abscess in developed countries
Clinical features and investigation
- The clinical features are non-specific and the diagnosis may be
delayed
- Symptoms and signs include
- Flank, back or abdominal pain
- Fever
- A limp
- Malaise and weight loss
- Lump in the groin
- The WCC and inflammatory markers may be raised
- Plain abdominal x-ray may be normal
- Ultrasound has a sensitivity of only 60%
- CT is the gold standard
- MRI may be useful
Management
- Management involves
- Appropriate antibiotics based on the likely cause
- Drainage of the abscess
- Antibiotics can be changes when sensitivities are knows
- Drainage can be achieved percutaneously or by surgery
- Surgery may be more appropriate in secondary abscesses
- The underlying pathology may require surgical correction
Bibliography
Abraham N, Doudle M, Carson P. Open versus closed
treatment of abscesses. a controlled clinical trial. Aust NZ J
Surg 1997; 67: 173-176.
Mallick I H, Thoufeeq M H, Rajendran T P. Iliopsoas
abscess. Postgrad Med J 2004; 80: 459-462.
Venbrux A C, Ignacio E A, Soltes A P et al. Role of
the interventional radiologist in the management of abdominal abscess.
Adv Surg 2005; 39: 121-135. |